The invention relates to measures for processing received broadcast signals, in particular for sets for receiving and reproducing television signals.
For optimum videotex data coding, for error-free functioning of so-called descramblers andxe2x80x94not leastxe2x80x94for the impression of improved detail resolution on the screen of a television set of displayed pictures, it is known to process the video frequency response by influencing the higher frequency components in the video signal spectrum. For this purpose, means which act on the video frequency response in a correspondingly selective manner are provided in the video-signal-processing section of a television set.
The channel fine tuning of the relevant set can be used effectively as another means, in particular in the case of so-called tuner tilt. This channel tuning, which in principle effects frequency detuning of the tuner and results in corresponding shifting of the vision carrier on the Nyquist slope of the transmission curve, is not familiar to everybody, however. Furthermore, such tuner tuning also does not seem appropriate since today""s television sets are in any case provided with a transmitter search with automatic tuner tuning to the television channels which can be received, PLL (phase-locked loop), based tuning systems and storable channel frequency tables being provided for the tuners.
The object of the invention, therefore, is, in television sets, to simplify processing of the video frequency response by means of tuner tuning.
The invention is based on the idea, in the case of set programme location allocations that, in particular, are to be carried out by the customer for each television channel, of adaptation to a video frequency response sought in each case being carried out automatically by means of corresponding shifting of the vision carrier relative to the IF total transmission curve.
The respective adaptation for the relevant television channel of the set is effected, in principle, by the addition of a corresponding correction value to the corresponding channel tuning voltage of the tuner. In this casexe2x80x94for a first and for a second embodimentxe2x80x94the adaptation can be carried out according to the invention in a dynamic manner (i.e. by the addition of a correction value which is derived from a control or, for the second embodiment, is obtained by means of a control to the channel tuning voltage of the tuner), orxe2x80x94for a third embodimentxe2x80x94by the addition of a correction value which is determined beforehand (e.g. during the installation of the set at the customer""s premises) and stored to the channel tuning voltage.
As a criterion for the video frequency response, it is advantageously possible to use, in particular for the first embodiment, the colour burst of the respective transmitted television signal, the said colour burst serving for automatic colour contrast control (Automatic Colour Control). For the first embodiment, the control voltage fed to the colour control amplifier during the colour contrast control is in this case simultaneously utilized as a correction value, in which case merely corresponding level adaptations may be necessary.
Furthermore, a measurement signal designed as a 2T pulse or a measurement signal designed as a multiburst having a correspondingly large video frequency can advantageously be utilized as a criterion for the video frequency response, in particular for the second and third embodiments. Such a measurement signal, with which the respective vision carrier is modulated, is concomitantly transmitted in any case e.g. in accordance with the CCIR Standard for television signals as a test line in these signals.
In the second embodiment, the correction value of the relevant channel is obtained by comparing the measurement signal with a reference value. According to the invention, such reference values are adapted to the respective set design. They are preferably specified e.g. during the set manufacturing process, in the course of the programming of the set xcexcP of the relevant television set, and stored.
In order to obtain the video frequency response sought in the relevant channel, for the third embodiment it is provided that the correction value is determined from the measurement of the measurement signal with corresponding shifting of the vision carrier relative to the IF total transmission curvexe2x80x94e.g. by means of the channel fine tuning of the tunerxe2x80x94and is subsequently stored.
The respective storage for correction and reference values is designed to be overwritable so that, if appropriate, changes can later be made, e.g. by after-sales service on the customer""s premises. In this case, the same also applies correspondingly to the first embodiment with regard to a later change of level adaptations performed in the set manufacturing process.
The invention thus has the advantage that it is possible to compensate not only for the effects on the video frequency response which are caused by tolerance-dictated tuner tilts and/or tolerance-dictated deviations of the selection means in the IF range but also for those effects which are to be attributed to incorrect adaptations between television set and antenna system, or between television set, converter (such as e.g. also so-called satellite receivers) and antenna system.
Further advantages emerge from the description below. The invention is explained in more detail with reference to the drawing, in which: